I just signed up for a free trial of Constant Contact to use for email marketing.

I'm excited about it because it allows you to communicate directly to your current clients and interested prospects.  Advertising can be too expensive.  Press releases and articles can get the word out, but the piece needs to be accepted by an editor, and editors only publish stories that meet the needs of their publication.

Sending out e-newsletters gives you more control, because you are the editor, and you know your audience is open to your message (because they signed up to get your newsletter).